Static induction regulator employing transformers with even-harmonic feedback



14,1967 F. A. WENTWORIVTH. 3,353,094

STATIC INDUCTION REGULATOR EMPLOYING TRANSFORMERS Filed May 1, 1964 WITHEVEN-HARMONIC FEEDBACK 4 Sheets-Sheet 1 COMBINED m SINGLE WINDING INPUTVOLTAGE l4 OUTPUT l8 VOLTAGE Nov. 14, 1967 Filed May 1, 1964 LINE F A.WENTWdRTH 3,353,094

4 Sheets-Sheet 2 LOAD Nov. 14, 1967 F w wo T 3,353,094

STATIC INDUCTION REGULATOR EMPLOYING TRANSFORMERS WITH EVEN-HAR'MONICFEEDBACK Filed May 1, 1964 4 Sheets-Sheet 5 LOAD Nov. 14, 1967 F. A.WENTWORTH 3,353,094

STATIC INDUCTION REGULATOR EMPLOYING TRANSFORMERS WITH EVEN-HARMONICFEEDBACK Filed May 1, 1964 4 Sheets-Sheet 4 VQLTAGE FIG] BY WM,WWM

ATTdRA/EYS United States Patent 3,353,094 STATIC INDUCTION REGULATOREMPLOYING TRANSFORMERS WITH EVEN HARMONIC FEEDBACK Fitzwilliam A.Wentworth, Mosmau, New South Wales, Australia, assiguor to Stabilac Pty.Limited, Kingsgrove, New South Wales, Australia, a corporation of NewSouth Wales, Australia Filed May 1, 1964, Ser. No. 364,198 Claimspriority, application Australia, May 21, 1963, 30,912/ 63 Claims. (Cl.323-45) ABSTRACT OF THE DISCLOSURE The static induction regulator of thetype which employs two transformers with their primaries connected inseries to an AC. power source, their secondaries connected in series inopposition so that under normal conditions the secondary voltages areequal and opposite, and control windings on the transformers such thatwhen control currents are applied to the control windings the secondaryvoltage from one transformer (e.g. the boost transformer) increases thesecondary voltage from the other transformer (e.g. the buckingtransformer) decreases, has each transformer constructed with two fiuXpaths, and with windings which are connected to a rectifier to provideeven harmonic feedback. The second harmonic feedback windings can becombined with either the control windings or the primary windings. Inthe latter case the primary windings are divided.

This invention relates to apparatus for static magnetic control of AC.power. It is of particular application to AC. voltage stabilising andregulating systems of high power handling capacity. Since theperformance and characteristics of the device are very similar to thoseof the induction regulator it will hereinafter be called a StaticInduction Regulator.

Apparatus in accordance with the invention is an improvement over otherknown magnetic systems in that a bucking or boosting voltage isintroduced in series with the line, and the magnitude and phase of thisvoltage may be controlled to either add to or subtract from the supplyvoltage. Further, this voltage is derived from a source having good loadregulation characteristics, and is capable of providing a fast response.

The following advantages also result:

( 1) Very high electrical efficiency.

(2) Good input power factor.

(3) Efiicient utilisation of materials with consequent low weight andsmall size.

(4) Low distortion.

(5) Fast response time and low control power requirements.

(6) Better performance for transient line voltages than equipments usingseries connected magnetic regulating elements.

An object of this invention is to provide a static induction regulatorin which two transformers have their primaries connected in seriesacross an AC. power supply line and their secondaries connected inseries with each other and the line, the outputs from the twosecondaries opposing one another, each transformer having two separateor divided flux paths, even harmonic feedback Windings on eachtransformer so connected that even-order harmonic components are inducedin them, said last-mentioned windings being shunted by rectifyingelements, control windings on each transformer, and means for apply-3,353,094 Patented Nov. 14, 1967 ing control currents to the controlwindings in such sense that as the secondary winding voltage from onetransformer increases the secondary winding voltage from the othertransformer decreases.

For the purposes of this description each transformer with itsassociated feedback and control winding will be termed a controlledsaturable transformer and the sys tern as a whole will comprise two ofthese for a single phase supply.

Each controlled saturable transformer has inherent constant voltagecharacteristics, and the voltage at which they saturate may be varied bya control circuit provided in association with each primary. A conditionmay be set up by the application of a particular control current to eachprimary, such that the sum of the individual primary saturation voltageis equal to, or is slightly lower than the line voltage. As a result ofthe constant voltage characteristics of each primary the voltage acrosseach will be approximately equal and this balanced condition will beonly slightly affected by the load. Under these circumstances the commonsecondary winding will have practically no voltage induced in it, andthe load voltage will be equal to the line voltage less a slightregulation drop.

Now if the control current to the bucking primary is increased, whilstthat to the boosting primary is decreased the voltage distributionacross the primaries will no longer be equal, the higher voltageappearing across the boosting primary. Under these conditions theresultant voltage induced in the common secondary will boost the linevoltage. Maximum boost will be obtained when the control current to thebucking primary is a maximum, whilst that to the boosting primary hasbeen reduced to zero. Reversal of the control condition will result in aload voltage lower than that of the incoming line. Odd order harmoniccomponents will be present across whichever primary is controlled intosaturation, but since this primary contributes a proportionately lowervoltage to the total secondary the waveform of the output voltage is notseriously distorted.

The control current may be D.C., A.C., double frequency A.C., half waverectified A.C., or a combination of these. Control may be achieved byvariation of amplitude, or phase shift, or alternatively by modificationof the feedback rectifier characteristics. In general, control by halfwave elements leads to a simple and economical system.

The physical arrangement of windings and cores may take one of a largenumber of mechanical forms, and is readily adaptable to standard coreforms used for transformer manufacture.

Reference will now be made to the accompanying drawings in which FIGURE1 is a diagrammatic showing of a form which the two controlled saturabletransformers may take,

FIGURE 2 is a section through a core and winding assembly showing aphysical form which the arrangement of FIGURE 1 may take,

FIGURE 3 is a circuit diagram of an arrangement in which the controlledsaturable transformers of FIGURE 1 are connected as a static inductionregulator according to the invention, and in which means are provided tocontrol a voltage across a load,

FIGURE 4 is a circuit diagram of a static induction regulator using thecontrolled saturable transformers of FIGURE 1 which is generally moresuited to a voltage stabiliser,

FIGURE 5 shows a diagram of a single-phase line-voltage stabiliser usingthe static induction regulator of FIG- URE 4,

FIGURE 6 shows an alternative arrangement of windings on the cores ofthe controlled saturable transformers, and

FIGURE 7 shows, a modification of FIGURE 6.

FIGURE 1 shows diagrammatically the preferred form which the twocontrolled saturable transformers I, 11 may take, and the manner inwhich the windings are interconnected, while FIGURE 2 is a sectionthrough a core and winding assembly showing a physical form which theassembly of FIGURE 1 may take. Each transformer I, II has a divided orseparate pair of flux paths 6A, 6B

and 11A, 11B, respectively. The main or primary windings 3A, 3B, 3C, 3Dand 8A, 8B, 8C 8D respectively of the two transformers are each wound infour sections to provide two parallel current paths, namely 3A, 3B and3C, 3D for transformer I and 8A, 8B and 8C, 8D for transformer II.Rectifiers 7 and 12 are connected between points on the two primariesrespectively of equal potential with respect to fundamental frequenciesand odd order harmonics. Thus rectifier 7 is connected between thejunction of 3A, 3B and the junction of 3C, 3D. When so connected the twoprimary windings also opcrate as even harmonic feedback windings.

' Each core pair 6A, 6B and 11A, 11B carries a secondary winding 4A, 4Band 9A, 9B. The two secondaries are connected in series, phased asshown, and are connected to terminals 13, 14. Each core pair is alsoprovided with a control winding A, 5B and 10A, 1013 respectively whichwindings connect to terminals 15, 16 and 17 and 18 respectively. Controlcurrents are supplied to the control windings 5A, 5B and 10A, 10B so asto provide a controllable and non-symmetrical or unidirectionalcomponent of magnetic flux in the individual core pairs. Under theseconditions each transformer primary will exhibit constant voltagecharacteristics. The electrical operating principles of each controlledsaturable transformer which lead to their constant voltagecharacteristic is described in United States Patent No. 3,253,212. Whenconnected in series across a source of alternating voltage the voltagedistribution between primaries will be a function of the flux componentsproducing even order harmonics in the individual core pairs.

FIGURE 3 is a circuit of an arrangement using the controlled saturabletransformers of FIGURE 1 which accepts a fixed input voltage at theterminals 1, 2 and provides a voltage across a load L which iscontrollable over a range. The two secondaries 4, 9-, which are eachshown as a single winding in this drawing, are connected in series witheach other and with the line 1, 2 and load L. The primaries are phasedso that one provides a secondary voltage in phase with the supply, aboosting voltage, and the other provides a secondary voltage 180 out ofphase-with the supply voltage, a bucking voltage. The vector sum of theindividual primary saturation voltages is set to be approximately equalto the supply voltage by passing the same control current through eachcontrol winding 5A, 5B, 10A, 10B and increasing this current until theAC. primary magnetising current is just over the knee of the saturationcurve. In the circuit of FIGURE 3 this current is provided by thebattery 23. Since each primary has been controlled to the same extentthe open circuit output voltage will be equal to the input voltage.Further for changes of load the output voltage regulation will be low,since the voltage across either primary cannot rise without drawing aheavy magnetising current.

To provide for either a boost or buck condition the control currents areunbalanced by displacing the moving arm 25 of the potentiometer 24. Therectifiers 19, 20 and resistors 21, 22 are included to limit loading ofthe evenharmonic components present across the control windings by thelow control source impedance.

In FIGURE 3 the control current has been shown for purposes ofillustration as a direct current. However, since the primary saturationvoltages are dependent on both control current and line frequency, it isdesirable that the control current be made frequency dependent if theequipment is required to operate over a range of frequencies. Forexample, the control current could be supplied from a constant voltagetransformer or through a series connected capacitor. I

FIGURE 4 illustrates a connection of a static induction regulatorgenerally more suited to a voltage stabiliser where the output voltageis to remain constant for variations of input voltage and load. The twotransformers I, II are again the two transformers of FIGURE 1 but areshown diagrammatically as in the case of FIGURE 3. The windings areconnected in the same manner as in FIG- URE 1 but, as was also done inthe case of FIGURE 3, the secondaries 4, 9 have each been shown as asingle winding whereas in fact each consists of the two windings 4A, 4Band 9A, 9B respectively, as shown in FIGURE 1. Also as in the case ofFIGURE 3 the secondary windings 4, 9 are connected so as to oppose eachother, one secondary winding providing a BOOST voltage and the other aBUCKING voltage. The only difference between the arrangement of thetransformers in FIGURES 3 and 4 is that in FIGURE 4 the secondarywindings 4, 9 are connected ahead of the primary windings with respectto the input line, whereas in FIGURE 3 the primary windings appeardirectly across the input line. Control terminals 15, 16 and 17, 18 ofFIGURE 4 may be connected to the similarly numbered control terminals ofFIGURE 3, but an alternative automatic control arrangement is shown inFIGURE 5 where transistors are used as control elements. In thisarrangement the voltage across whichever primary is heavily controlledis substantially in quadrature with the output voltage. Further it maybe readily arranged that this phase angle is constant for variousloadings, and that consequently the phase relationship of the A.C.component of an unsmoothed DC. control current may also be constant.Another advantage of this connection is that the total primary voltageis constant.

FIGURE 5 shows a diagram of the static induction regulator applied to asingle-phase line-voltage stabiliser. The two controlled saturabletransformers have. been. shown diagrammatically, the primaries beingnumbered 3 and 8 respectively, the control windings 5 and 10respectively, and the secondary windings being combined in a singlewinding, numbered 4 and 9, by appropriate phasing of primary and controlwindings. The physical construction of such an induction regulator isillustrated by FIGURE 2. The control windings 5, 10 are supplied from afull-wave rectifier 29, 30 and transformer 31, and the currentsarevaried differentially by control of the transistors 26;, 27. Theprimary of the transformer 31 is connected to the output voltage througha phase-shifting capacitor 32 chosen to give optimum phasing of thecontrol currents (approx. lead). A second transformer 33, with itsprimary sensing the output voltage, is cons nected to avoltage-sensitivebridge 34 which in turn supplies an error signal to the differentialamplifier 35. The

resistor 28 is chosen to make the total primary saturation voltageslightly higher than the output voltage. Where the output voltage isrequired to have an extremely pure waveform harmonic filters may beinterconnected with the main windings of the induction regulator.

One alternative arrangement of windings on the controlled saturabletransformers is shown in FIGURE 6 where primaries 3, 8 and secondaries4, 9 are wound on the centre legs of shell type laminations. WindingsSA, 5B and 10A, 10B are wound on the two divided flux paths 6A, 6B and11A, 11B, respectively, and are phased to cancel voltages of fundamentalfrequency and odd order harmonies. They are shunted by rectifyingelements 7, 12 and operate simultaneously as feedback and controlwindings. It will be seen that the arrangement of the two transformershas primary terminals 1, 2, secondary terminals 13, 14, and controlterminals ls, 16 and 17, 18, all of which corresponds to the similarlynumbered terminals of FIGURE 1. The arrangement of FIGURE 6 can replacethe arrangement of FIGURE 1 in the circuits of FIG- URES 3, 4 and 5directly by connecting the terminals 1, 2, 13, 14, 15, 16, 17 and 18 ofthe arrangement of FIG- URE 6 to the same numbered terminals in FIGURES3, 4 and 5, after removing the transformers of FIGURE 1 from thecircuit.

If desired separate control and even-harmonic feedback windings may beused. In all the arrangements described the relationships of the primaryand secondary windings can be reversed.

Whilst, in the interests of simplicity, the operating principles havebeen described for a single phase unit, similar considerations willapply for polyphase operation, and the invention is equally applicableto polyphase as to single phase operation.

FIGURE 7 shows a variant of the circuit arrangement of FIGURE 6 in whichthe two transformers each have ever-harmonic feedback windings 42A, 42Band 43A, 43B respectively which are separate from the control windings40A, 40B and 41A, 41B respectively. The control windings 40A, 40Bconnect to terminals 15, 16, as did the windings 5A, 5B of FIGURE 6 andthe control windings 41A, 41B connect to terminals 17, 18 as did alsothe windings A and 10B of FIGURE 6. The primary and secondary windings3, 8 and 4, 9 respectively of FIGURE 7 are positioned and connectedsimilarly to those of FIGURE 6, and are similarly numbered. It isthought that the operation of the embodiment of FIGURE 7 will be obviousfrom the above description and that of FIGURES 6 and 3. It will be seenthat the control terminals 15, 16, 17, 18 have been connected to amanual current control comprising battery 23, potentiometer 24,resistors 21 and 22, and rectifier 19, 20 which is the same control asis used in FIGURE 3, and whose operation will be evident from thedescription of that figure.

What I claim is:

1. A static induction regulator comprising input terminals to theregulator, output terminals to the regulator, two transformers, a threelegged core for each transformer consisting of a central limb and twoouter limbs, a primary winding for each transformer on the central limbthereof, series connections between the primary windings, a secondarywinding for each transformer on the central limb thereof, seriesconnections between the secondary windings and the input and outputterminals such that the secondary voltages oppose each other, a controlwinding for each transformer having portions on each outer limb, arectifier connected across each control winding whereby it functions asa second harmonic feedback winding, means for applying currents throughsaid control windings such that the two secondary voltages are equal andopposite, and means for varying the currents through the controlwindings such that as one secondary winding voltage increases the othersecondary winding voltage decreases.

2. A static induction regulator comprising input terminals, outputterminals, t-wo transformers, an iron core for each transformer having acentral leg and two outer limbs, a primary winding on the central leg ofeach transformer, series connections of the primary windings to theinput terminals, a secondary winding 0n the central leg of eachtransformer, series connections of the secondary windings between theinput and output terminals so that the secondary voltages oppose eachother, a pair of even-harmonic feedback windings, one on each outer limbof the core for the first transformer, connected in opposition withrespect to voltages of fundamental frequency induced in them, a firstrectifier connected in shunt with the evenharmonic feedback windings, asecond pair of even-harmonic feedback windings, one on each outer limbof the core for the second transformer, connected in opposition withrespect to voltages of fundamental frequency induced in them, a secondrectifier connected in shunt with the second pair of even-harmonicfeedback windings, a first pair of control windings, one on each outerlimb of the core of the first transformer, similarly connected inopposition, a second pair of control windings, one on each outer limb ofthe core of the second transformer, similarly connected in opposition,and means for applying control currents to the control windings suchthat as the secondary voltage of the first transformer increases thesecondary voltage of the second transformer decreases.

3. A static induction regulator comprising input terminals, outputterminals, two transformers, an iron core for each transformer having acentral leg and two outer limbs, a primary winding on the central leg ofeach transformer, series connections of the primary windings to theoutput terminals, a secondary winding on the central leg of eachtransformer, series connections of the secondary windings between theinput and output terminals so that the secondary voltages oppose eachother, a pair of even-harmonic feedback windings, one on each outer limbof the core for the first transformer, connected in opposition withrespect to voltages of fundamental frequency induced in them, a firstrectifier connected in shunt with the even-harmonic feedback windings, asecond pair of even-harmonic feed back windings, one on each outer limbof the core for the second transformer, connected in opposition withrespect to voltages of fundamental frequency induced in them, a secondrectifier connected in shunt with the second pair of even-harmonicfeedback windings, a first pair of c0ntrol windings, one on each outerlimb of the core of the first transformer, similarly connected inopposition, a second pair of control windings, one on each outer limb ofthe core of the second transformer, similarly connected in opposition,and means for applying control currents to the control windings suchthat as the secondary voltage of the first transformer increases thesecondary voltage of the second transformer decreases.

4. A static induction regulator comprising input terminals, outputterminals, two transformers, an iron core for each transformer having acentral leg and two outer limbs, a primary winding on the central leg ofeach transformer, series connections of the primary windings to theinput terminals, a secondary winding on the central leg of eachtransformer, series connections of the secondary windings between theinput and output terminals so that the secondary voltages oppose eachother, two similar windings, one on each outer limb of the core of thefirst transformer, connected in opposition with respect to voltages offundamental frequency induced in them, a rectifier connected in shuntwith the said two similar windings, a second pair of similar windings,one on each outer limb of the core of the second transformer, connectedin opposition with respect to voltages of fundamental frequency inducedin them, a second rectifier connected in shunt with the said second pairof similar windings, means for applying control currents to the said twopairs of similar windings such that the two secondary voltages are equaland opposite, and means for varying the control currents so that as onesecondary voltage increases the other secondary voltage decreases.

5. A static induction regulator comprising input terminals, outputterminals, two transformers, an iron core for each transformer having acentral leg and two outer limbs, a primary winding on the central leg ofeach transformer, series connections of the primary windings to theoutput terminals, a secondary winding on the central leg of eachtransformer, series connections of the secondary windings between theinput and output terminals so that the secondary voltages oppose eachother, two similar windings, one on each outer limb of the core of thefirst transformer, connected in opposition with respect to voltages offunof similar windings, one on each outer limb of the core of the secondtransformer, connected in opposition with respect to voltages offundamental frequency induced in them, a second rectifier connected inshunt with the said second pair of similar windings, means for applyingcontrol currents to the said two pairs of similar windings such that thetwo secondary voltages are equal and o posite, and means for varying thecontrol currents so that as one secondary voltage increases the othersecondary voltage decreases. 1

References Cited UNITED STATES PATENTS 1,485,727 3/ 1924 Sindeband 323452,351,980 6/1944 Lee 323-45 2,758,162 8/1956 Tekosky 323-56' X 8 Bennett323-56 Holt 323-56 Kernick et a1 32389.12 Chegwidden 323-56 Moyer 32348Wentworth 323-48 X JOHN F. COUCH, Primary Examiner.

A. D, PELLINEN, Assistant Examiner.

1. A STATIC INDUCTION REGULATOR COMPRISING INPUT TERMINALS TO THEREGULATOR, OUTPUT TERMINALS TO THE REGULATOR, TWO TRANSFORMERS, A THREELEGGED CORE FOR EACH TRANSFORMER CONSISTING OF A CENTRAL LIMB AND TWOOUTER LIMBS, A PRIMARY WINDING FOR EACH TRANSFORMER ON THE CENTRAL LIMBTHEREOF, SERIES CONNECTIONS BETWEEN THE PRIMARY WINDINGS, A SECONDWINDING FOR EACH TRANSFORMER ON THE CENTRAL LIMB THEREOF, SERIESCONNECTIONS BETWEEN THE SECONDARY WINDINGS AND THE INPUT AND OUTPUTTERMINALS SUCH THAT THE SECONDARY VOLTAGES OPPOSE EACH OTHER, A CONTROLWINDING FOR EACH TRANSFORMER HAVING PORTIONS ON EACH OUTER LIMB, ARECTIFIER CONNECTED ACROSS EACH CONTROL WINDING WHEREBY IT FUNCTIONS ASA SECOND HARMONIC FEEDBACK WINDING, MEANS FOR APPLYING CURRENTS THROUGHSAID CONTROL WINDINGS